Nowadays, electrical apparatuses, such as transformers, autotransformers, or reactors are immersed in one or more liquid or gaseous fluids or combinations of both to ensure their electrical isolation or refrigeration. Therefore, in order to keep those electrical apparatuses immersed in one or more fluids, it is required to be contained in a structure called a tank. The fluids currently used for this purpose are liquids, such as oil or askarel, or gases, such as nitrogen, air or fluorine gases. So, hereafter the term fluid will be used to name them and any other liquid or gas, or a combination of both acting as isolation and/or refrigerant for those electrical apparatuses.
Conventional tanks for an electrical apparatus are generally cube-shaped or rectangular-parallelepiped structures that consist substantially of four vertical lateral walls, one lower wall or horizontal base, and one higher wall or horizontal cover. During the assembling, these walls are joined to each other by welding lines and reinforced through support members of a plurality of channel type or bed type, welded in vertical or horizontal positions throughout the flat surface of each wall.
In certain types of electrical apparatuses immersed in fluid, depth, width and length of the internal tank are controlled by the free electrical and mechanical space that is necessary to keep between the internal flat surface of the walls and the external surface of the core and the transformer windings immersed in the tank. Therefore, the internal volume of a cube or parallelepiped tank ends up being very large, so minimal distance required is over-estimated between the internal surfaces of the walls and the external surface of the core and windings mostly, which at the same time increase the quantity of liquid or gaseous fluid required. Being necessary, in some cases, support members are added to prevent deformation of the lateral walls and base because of internal and external pressures.
One way to avoid adding reinforcing elements welded in the tank is to build the lateral walls with one or more trapezoid-shaped undulations, as described by BBC AG. Brown, Boveri & Cie in the Spanish utility model ES-208,369. The restriction of this proposal is that it does not eliminate the welded supports at all because they can require a channel-type support welded in the large wall sides. At the same time, the free electrical and mechanical space required is still over-estimated between the internal surfaces of the walls and the external surface of the core and windings. In addition, angled corners are formed between the joins of lateral walls, and if the walls have more than one undulation, the tank requires more liquid or gaseous fluid to refill such undulations.
One way to avoid adding reinforcing elements welded to the tank is to build short curve-shaped lateral walls, just as Ito Tatsuo describes in the publication of the British patent application GB-2,050,069. The restriction of this proposal is that it only eliminates the welded supports in the short lateral walls because they are curved, but in the long lateral walls one or more reinforcing welded elements are still required.
Another current tank proposal applied to a transformer is described by Masahiro Kobayashi in the Japanese patent JP-61,135,104. The disclosure describes a tank made up of long lateral walls with one or more curved undulations and the short lateral walls curve-shaped. The restriction of this proposal is that it requires high-precision machinery for its manufacturing, and even so it requires vertical supports welded between the long lateral walls. At the same time, the joint between a long lateral wall and a short lateral wall forms an angled corner.
According to the previous description, which reflects the restrictions of the current tanks for electrical apparatuses immersed in fluids, it is then necessary to offer an easy-to-manufacture tank that eliminates welded support elements, and reduces the isolation and refrigerant fluid volume required, making the tank as small as possible in accordance with the core dimensions and windings, and other connectors and electrical accessories that will be contained within.